C: Good Habits re: Transitioning to C++

The best advice is probably to treat them as completely separate languages. Yes, most C code can be compiled by a C++ compiler, but it's generally not a good way to go.

C is very much a low-level hackery language. What you see is what you get. It has pointers and structs, so you use pointers and structs. It has very little type safety, so you ignore type safety as much as possible.

C++ on the other hand, allows a huge number of abstractions. Rather than pointers, you'll typically want to use iterators, which behave conceptually as pointers, but aren't (or might not be).

Instead of throwing away type information (for example having functions accept a void* so they'll work with any pointer type), you can use templates to retain type safety and still be able to reuse the same single function definition.

And you're given an excellent standard library which enables you to express complex algorithms in terms of simple predefined building blocks.

C++ is a multi-paradigm language. Some answers here have said that C++ is object-oriented, which is partially true. It does have support for object-oriented code, yes, but that's not what C++ is.

C++ also has support for generic programming, which is often preferable over OOP. It has some limited support for functional programming as well. And of course, it still has support for C-style procedural programming as well. The trick in C++ is to understand all of these, so you know which to use when. That is C++'s strength, the ability to switch between and mix all these paradigms. People who call C++ an OOP language miss the point just as much as people who call it an improved C. It allows you to write code in either of these styles, but neither of these are really worthwhile in themselves. C is a better C-like language, and there are plenty of better OOP languages. If you want to stick to one single paradigm, use a language designed for that.